1. Field of the Invention
The present invention relates to a bass compensation device for, when a sound signal is reproduced by using a compact speaker, a headphone, or the like, compensating insufficient bass reproduction resulting from a narrow reproducible band of the bass side and realizing the reproduction of rich deep bass, and also relates to a sound system using this device.
2. Description of the Prior Art
The frequency ranges of sound signals input from a sound source are generally wider than the reproducible frequency range of a speaker in use. Therefore, in order to reproduce sound signals input from the sound source faithfully, it is necessary to provide a speaker having as wide a reproducible frequency range as possible. Each speaker has its own reproducible frequency range depending on its size and structure; in general, compact speakers have higher limits of reproducible frequency ranges at the bass side, thereby deteriorating the reproduction characteristic of bass.
However, speakers or headphones which are applied to portable devices like portable (note-type) PC or portable audio reproduction devices, to compact audio systems whose concept is space saving, and to car audio systems to be installed in a limited space inside a car have been expected to be as compact and lightweight as possible because of the limitation of their installing sites, and other reasons. This sacrifices the reproduction properties of bass, causing users to complain about insufficient reproduction of bass.
In order to solve these problems, conventional audio systems have a bass intensifying circuit built therein to compensate a low frequency component. FIG. 8 is a block diagram showing an example of the conventional bass intensifying circuits. The bass intensifying circuit having this structure is disclosed, for example, in Japanese Laid-Open Patent Application No. H08-237800.
As shown in the drawing, the conventional bass intensifying circuit includes an adder 80 that adds an L channel component LIN and an R channel component RIN of a input sound signal; a first low pass filter 81 (hereinafter referred to as the first LPF 81) that extracts a tone component lower than the reproduction limit of the speaker in use from the output signal of the adder 80; a full wave rectifier 82 that full-wave rectifies output signal A′ of the first LPF 81; a second low pass filter 83 (hereinafter referred to as the second LPF 83) that extracts only second harmonics from output signal B′ of the full wave rectifier 82; an amplifier 84 that amplifies output signal C′ of the second LPF 83, and adders 85, 86 that add output signal D′ of the amplifier 84 to the L channel component LIN and the R channel component RIN of the sound signal, thereby generating an L channel component LOUT and an R channel component ROUT for output.
FIG. 9 is a time chart showing waveform examples of output signals A′, B′, and D′. As shown in the drawing, when a sound signal is input into the bass intensifying circuit having the above structure, output signal D′ shapes a waveform which is twice the frequencies of output signal A′.
In the bass intensifying circuit having the above-mentioned structure, a low frequency component less than the reproduction limit of the speaker can be shifted to the frequency range of an octave higher to return to the original sound signal. Thus, the low frequency component which used to be absent can be compensated to realize powerful bass reproduction.
However, as shown in FIG. 9, the above-mentioned bass intensifying operation can be properly performed only when the second LPF 83 is in a steady state, whereas immediately after the sound signal is input or in the transition period immediately after the reception of the sound signal is completed, unnecessary DC components due to a transient phenomenon may be superimposed on output signal D′, thereby causing objectionable noise from the speaker.
An input sound signal may contain a super bass frequency component that cannot be inside the reproducible band of the speaker even if the frequencies are doubled. This may cause the speaker to have unnecessary vibration, thereby distorting the reproduced sound.
In the bass intensification by the conventional bass intensifying circuit, there are cases where the reproduction of a super low frequency component seems to be insufficient.
The conventional bass intensifying circuit having the above structure is not provided with means for removing a low frequency component less than the reproduction limit of the speaker from the input sound signal, which has the possibility of causing the speaker to have unnecessary vibration, thereby distorting the reproduced sound.